LaO_x(OH)_y supported platinum catalysts for CO oxidation:Deactivation by formation of lanthanum carbonate

Platinum catalyst for CO oxidation has been studied for decades,due to its high activity and good stability.In this work,we prepared three different lantha num oxide or hydroxide supports(LaO_x(OH)_y),and deposited platinum(Pt) with 0.5 at% via an impregnation approach to synthesize Pt/LaO_x(OH)_y catalysts.However,we find that these catalysts perform a poor stability for the CO oxidation reaction.The fresh and used samples were comprehensively characterized by multiple techniques including power X-ray diffraction(XRD),X-ray absorption fine structure(XAFS),transmission electron microscopy(TEM),temperature-programmed reduction by carbon monoxide(CO-TPR) and thermogravimetric analysis(TGA),to demonstrate that the oxidized platinum atoms or clusters,without any component of Pt-Pt metallic bond,are highly dispersed on the surface of LaO_x(OH)_y.Furthermore,the as-formed lanthanum carbonate(La_2 O_2 CO_3) during the exposure to ambient circumstances or in the reaction atmosphere of CO+O_2,severely impair the reactivity of Pt/LaO_x(OH)_y.On the basis of the obtained experimental results,we have drawn a conclusion that the oxidized PtO_x atoms or Pt_xO_y clusters are the active species for CO oxidation,while the formation of lanthanum carbonate is the origin of deactivation on reactivity.